The analysis of ECG waveforms using computerized arrhythmia monitoring systems consists of several steps. First each QRS complex must be detected and classified into a normal and abnormal categories. Subsequent analysis on the timing and pattern of these beats will yield alarms with several priorities to be annunciated to the user for treatment of the patient.
The patient population can be broken into two groups, patients with pacemakers and patients without pacemakers. Non-paced patients generate abnormal QRS complexes i.e. beats that are quite different in shape from their normal counterparts. However, paced patients generate paced beats initiated by the pacemaker that are treated as normal beats. These paced beats are substantially similar in wave shape to their abnormal counter-parts. Thus computerized arrhythmia monitoring systems designed for non-paced patients generate a high level of false alarms.
Some systems employ a simplistic approach to reduce false alarms by classifying any beat that is preceded by a pace pulse, as a paced beat. However this does not significantly reduce false alarms. Pace pulses can appear to be generated by noise in the ECG signals or be ineffective pace pulses that have not initiated any beat as to indicate an abnormal pacemaker operation. Such ineffectual pace pulses and false pace pulse indications may preceed abnormal beats which are misclassified as paced beats.
A group of similarly shaped QRS complexes, that are pacemaker initated, have pace pulses at a constant distance prior to the beats in this group.
The interval between the QRS complex and the preceding pace pulse is larger for atrially paced beats than ventricularly paced beats because of the delay in normal conduction of the pacing stimulus from the atrium to the ventricles. This relationship between atrial and ventricular pace pulse intervals to the QRS complex remains the same for dually paced beats.